[2/2] msvcirt/tests: Add initial tests for streambuf (try 2)

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
https://testbot.winehq.org/JobDetails.pl?Key=13771

Your paranoid android.


=== wvistau64 (64 bit msvcirt) ===
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=== w2008s64 (64 bit msvcirt) ===
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